A signal that is received or transmitted by a conventional wireless communications device in a wireless communications network is influenced by the surrounding environment. In theory, a conventional wireless communications device that has a single antenna 200 would have a radiation pattern as shown in a polar plot illustrated in FIG. 3. The single antenna 200 has an isotropic radiation pattern 210 illustrated with an isotropic gain line 220 of, for example, 0 dBi. Although radiation patterns are three dimensional, it is understood that the polar plots are merely two-dimensional representations. Thus, a polar plot may represent, for example, a cross section of a three-dimensional radiation pattern. In addition, the phrase “radiation pattern” is to be defined as including at least transmission patterns or reception patterns. The isotropic radiation pattern 210 is a theoretical, ideal model occurring, for example, in the remote vacuum of space with a point source of radiation.
In practical settings, for example, in an urban environment, multipath and other considerations create nonuniformities in the radiation patterns. A signal may bounce off, for example, the ground, buildings, walls or other reflecting structures before reaching the single antenna 200 of the conventional wireless communications device. Furthermore, since a signal may be scattered simultaneously across a plurality of paths in space and time before reaching the single antenna, the signal may interfere constructively and destructively with itself. FIG. 4 shows another polar plot illustrating an example of a multipath radiation pattern 260 including a gain line 230 generated from the single antenna 200. The gain line 230 has been distorted due to multipath interference. Thus, for example, points 240, 250, although equidistant from the single antenna, effectively see different radiation patterns in which the point 240 sees greater signal gain than the point 250.
Therefore, a user of the conventional wireless communications device, that is suffering from poor reception or transmission due to multipath conditions, typically may need to physically move around in a random search for an improved signal (e.g., move from the point 250 to the point 240 without knowledge of the shape of the radiation pattern 260). Such physical translations of the conventional wireless communications device are not convenient and may not even be available under certain conditions such as, for example, when the user may not be free to move around.
In addition, since multipath effects result, in part, from constructive and destructive interference of signals, multipath effects differ at different signal frequencies. Thus, for example, as shown in a polar plot illustrated in FIG. 5, a first gain line 270 is generated by the single antenna 200 at a first frequency f1 and a second gain line 280 is generated by the single antenna 200 at a second frequency f2.
The conventional wireless communications device may transmit and receive signals at different frequencies. Thus, for example, via the single antenna, the conventional wireless communications device may transmit at the first frequency f1 and receive at the second frequency f2. The conventional wireless communications device effectively experiences, for example, a radiation pattern for transmission as represented by the gain line 270 and a radiation pattern for reception as represented by the gain line 280. The consequences during, for example, two-way wireless communications between the single antenna 200 and a point 290 (e.g., a base station) are further illustrated in FIG. 5. The point 290 and the antenna 200 effectively experience disparate radiation patterns depending upon whether the single antenna 200 is transmitting or receiving. In this case, the single antenna 200 effectively experiences substantially more gain in receiving signals from the point 290 than in transmitting signals to the point 290. Thus, it is possible, for example, that although the signal from the point 290 is successfully received, the signal transmitted to the point 290 may be lost.